JP2010080957A - Method for generating laser and pulsed laser emission - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a Q switch laser so that the maximum pulse repetition rate is enhanced, and pulse length is maintained even a pulse repetition rate is increased, or shorter pulse length is selected. <P>SOLUTION: Laser for generating pulsed laser emission 2 includes: a resonator 3; a laser active medium 6 arranged in the resonator 3; and a Q switch 8 arranged in the resonator 3 and capable of setting a first state and a second state to set the quality of the resonator. The quality of the resonator is lower in a first state than that in a second state. The laser also includes: a detection unit 10 which measures the intensity of laser pulse during formation when the Q switch 8 is in the second state and outputs the measured value as an intensity signal I; and a control unit 11 which switches the Q switch 8 from the second state to the first state in response to a predetermined pulse period and the supplied intensity signal I before the completion of the pulse formation of the laser pulse, and controls the Q switch 8. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a Q-switched laser that generates pulsed laser radiation.

  Q-switched lasers have the disadvantage that the possible pulse repetition rate is relatively low. For this reason, for example, in a known Yb: YAG laser, the maximum pulse repetition rate is about 30 kHz. The pulse length of individual pulses of pulsed laser radiation also increases with increasing pulse repetition rate.

  U.S. Patent No. 6,057,031 describes a laser and a method for generating pulsed laser radiation. Patent Document 2 describes a solid-state laser and a method for adjusting the pulse energy of the solid-state laser.

German Patent Application Publication No. 10 2006 006 582 (A1) Specification German Patent Invention No. 196 34 969 (B4) specification

  Therefore, the object of the present invention is to provide a Q-switched laser so that the maximum pulse repetition rate can be further increased and the pulse length can be maintained even when the pulse repetition rate is increased or a shorter pulse length can be selected. It is to improve.

  The above objective is accomplished by a laser that generates pulsed laser radiation. The laser includes a resonator, a laser active medium disposed in the resonator, a first state and at least one second state disposed in the resonator and for setting a quality of the resonator. The Q switch and the quality of the resonator that can be set to be lower in the first state than in the second state, and when the Q switch is in the second state, the intensity of the laser pulse being formed is measured and the measured value The Q switch is switched from the second state to the first state in accordance with a predetermined pulse period and the supplied intensity signal before the pulse formation of the laser pulse is completed, and the Q switch is turned on. A control unit for controlling.

  This shortens the pulse period and can therefore be set to a desired value. Compared to the case where the pulse formation is not interrupted, the inversion level of the laser active medium remains high (for example 2 to 10 times, especially 3 to 5 times) when the pulse formation is interrupted. For this reason, a high pulse maximum output becomes possible.

  In particular, by using the laser of the present invention, the pulse period and the pulse repetition rate can be independently set over a wide range. Further, the maximum pulse repetition rate is significantly higher than that of a normal Q-switched laser in which pulse formation is not interrupted.

  In particular, in the laser of the present invention, the intensity value at the rise or fall of the laser pulse may be related to a desired pulse period. In this case, when the intensity value is reached, the Q switch is switched.

  In particular, in laser mounting, a Q switch switching period from the second state to the first state is considered in order to set a desired pulse period. The delay caused by the control electronics of the Q switch can also be taken into account.

The Q switch can be implemented as an acousto-optic modulator or an electro-optic modulator.
Further, in order to lengthen the maximum settable pulse period, the control unit can electronically delay switching of the Q switch from the second state to the first state.

  The laser can include a setting unit. The setting unit can input a predetermined pulse period and a predetermined pulse repetition rate, and is connected to the control unit. The control unit controls the Q switch so that the pulse laser radiation includes a pulse having a predetermined pulse period and a predetermined pulse repetition rate.

  Specifically, when a predetermined pulse period or a predetermined pulse repetition rate is input, the setting unit can display a possible pulse repetition rate or a possible pulse period for selection. For this reason, the laser which can set a pulse period and a pulse repetition rate easily is provided.

The setting unit may be implemented as hardware, software, or a combination thereof.
In particular, the laser also comprises a pump source for pumping the laser active medium.

The laser further includes elements well known to those skilled in the art necessary for the operation of the laser.
Furthermore, a resonator, a Q switch and a laser active medium disposed in the resonator are provided, and the Q switch can be set to a first state and a second state in order to set the quality of the resonator, The cavity quality provides a way to produce pulsed laser radiation in a laser that is lower in the first state than in the second state. In this method, when the Q switch is in the second state, the step of measuring the intensity of the laser pulse being formed and outputting it as an intensity signal, and the predetermined pulse period and the predetermined intensity before completing the pulse formation of the laser pulse The Q switch is switched from the second state to the first state according to the signal.

  By using this method, the pulse period and the pulse repetition rate can be independently set over a wide range in the Q-switched laser. In addition, the pulse repetition rate can be significantly increased as compared with a normal Q-switched laser.

Advantages of the inventive method are disclosed in the dependent claims.
It is to be understood that the features described above and those described below are useful within the scope of the present invention, not only in the disclosed combination, but also in other combinations or alone.

1 is a schematic diagram of an embodiment of a laser according to the present invention. Explanatory drawing of pulse generation. Another explanatory view of pulse generation. Explanatory diagram of possible pulse duration and possible pulse repetition rate.

The present invention will be described in detail below with reference to the accompanying drawings. The drawings also disclose essential features of the invention.
In the embodiment shown in FIG. 1, a laser 1 that generates pulsed laser radiation 2 comprises a resonator 3 that includes a high reflection end mirror 4 and a separation (decoupling) mirror 5. The separation rate of the separation mirror 5 is about 10%.

  A laser active medium 6 (Yb: YAG) is disposed in the resonator 3. The laser active medium 6 is pumped using the light from the pump light source 7 (continuously in this embodiment) (arrow P1).

  In the resonator 3, a Q switch 8 as an acousto-optic modulator and a polarizing mirror 9 are further arranged. The polarizing mirror 9 separates a small part of the reflected laser radiation. This portion is measured by the detection unit 10. The detection unit 10 is disposed behind the polarizing mirror 9 and outputs an intensity signal I.

  The laser 1 is supplied with an intensity signal I and can switch the acousto-optic modulator 8 between a low quality first state and a high quality second state, a desired pulse repetition rate and And a setting unit 12 capable of setting a desired pulse period.

  In the laser 1 of the present invention, a pulse having a set pulse period (hereinafter also referred to as an adjusted pulse) is generated as follows. When the acousto-optic modulator 8 is switched to the low-quality first state, no laser operation is observed due to high loss in the resonator, but an inversion distribution occurs at a desired level.

  When the acousto-optic modulator is switched to the high quality second state, the laser operation starts. If the acousto-optic modulator 8 remains in the second state for a sufficiently long time, a laser pulse 13 (unadjusted pulse) indicated by a dotted line in FIG. 2 may be generated.

However, the intensity in the resonator, and thus the intensity of the laser pulse 13 being formed, is continuously measured by the detector 10 and supplied to the controller 11 as an intensity signal I. Control unit 11 is designed to associate an intensity value I ₁ and the desired pulse duration. Thus, when reaching the intensity value I ₁ which gave the relationship at time t _2, the control unit 11 acousto - switching the optical modulator 8 from the second state to the first state. Here, since the loss in the resonator increases again, the pulse formation is interrupted, and a shorter pulse 14 having a higher maximum pulse output is output from the resonator 3.

A predetermined time ΔAOM elapses from when the switching signal for switching from the second state to the first state is supplied to the acousto-optic modulator 8 until the first state is reached. For this reason, the acousto-optic modulator 8 switches to the first state for the first time at time t ₃ . The time t ₃ or later is suspended actually pulse form, the pulse period is short pulses 14 than pulse 13 is generated. Since the inversion level remains high, a higher repetition rate (in this embodiment a repetition rate about 3 times higher than the unadjusted pulse 13) and a higher pulse stability are guaranteed.

What has become clear as an advantage is that the intensity is determined at the rise of the pulse 13 and that it is used as a measure of the pulse length to be set. Therefore, in the example described in this embodiment, the intensity values from time t ₁ to time t ₄ can be used for setting the desired pulse period. The range of the minimum possible pulse length is determined by the switching period ΔAOM. In the structure selected in this embodiment, the minimum pulse length is 100 ns to 200 ns.

The maximum settable pulse length t _max1 is determined by t ₄ and ΔAOM as shown in FIG. In this embodiment, the maximum pulse length t _max1 is about 700 ns.

  Of course, the pulse 13 and the pulse 14 do not occur simultaneously, but FIG. 2 shows that the pulse start times coincide with each other. For this reason, it can be estimated from the figure that the rising edge of the pulse 14 is steeper than the rising edge of the pulse 13. This is mainly because in the generation of the pulses of the present invention, the pulse formation is interrupted during the generation of each pulse, so that a higher inversion level persists in the resonator than if pulse 13 was generated without such adjustment. It depends.

FIG. 3 shows various laser pulses 14, 14 ₁ , 14 ₂ ,. . . 14 ₇ is shown. Each laser pulse 13, 14, 14 ₁ ,. . . 14 _7, indicated by the time axis t with respect to the trigger time. The trigger time is a time during which the acousto-optic modulator 8 is operated so as to switch from the first state to the second state. This trigger time is not shown.

Longest adjusted pulse 14 ₁ pulse period can be seen from FIG. Is a pulse shape that closely resembles the unregulated pulse 13. It is clear that the pulse generation was interrupted by the sudden drop seen in the middle of the fall.

Pulses 14 ₂ , 14 ₃ ,. . . As 14, 14 ₇ and the pulse duration is shortened, increasing the pulse maximum output (higher pulse), time to pulse generation start to decrease for the trigger time (pulse "displacement" to the left in FIG. 3). This behavior is due to the high inversion level being maintained as described above.

  FIG. 4 shows a possible pulse width (vertical axis) in relation to a settable repetition rate (horizontal axis). A curve K1 in FIG. 4 shows a case where the pulse width is not controlled. In this case, the acousto-optic modulator 8 switches from the second state to the first state only when the pulse generation is completed during the generation of the pulse 13. As can be inferred from the curve K1, pulse repetition rates in the range of 8 kHz to 30 kHz are possible.

  A range B1 shown in FIG. 4 is a pulse width range that can be set by using the interruption of pulse generation according to the present invention. Although pulse widths in the range of 200 ns to 700 ns are possible, a much higher pulse repetition rate can be set than in the generation of the unadjusted pulse 13. This is mainly because when the pulse period is shortened by interrupting the pulse formation as described above, the inversion level maintained in the laser active medium 6 is higher than when the pulse formation is not interrupted, and as a result, This is because, since the high inversion level is maintained, the pulse repetition rate can be significantly increased, while a very stable pulse can be obtained.

The pulse repetition rate and pulse width can be freely selected within a range B1 schematically shown in FIG.
In the laser 1 of the present invention, the control pulse width of the pulse 14 can be increased. In addition to the existing modulator switching period ΔAOM, an electronic delay ΔR is introduced by using the control unit 11. This results in a longer maximum pulse period t _max2 as schematically shown in FIG. This longer pulse period includes a range B2 indicated by hatching in FIG. As a result, a pair of pulse period and pulse repetition rate values within this range can be set, and B1 and B2 are included.

In particular, the setting unit 12 is implemented to present for selection a pulse repetition rate (depending on the range B1 and optionally on the range B2) that is possible in this pulse period when the desired pulse width (ie pulse period) is input. May be. The pair of the selected pulse period and pulse repetition rate value is supplied to the control unit 11 via the setting unit 12, and the acousto-optic modulator 8 operates according to this. This results in a pulse 14 of pulsed laser radiation 2 having a desired pulse duration and a desired pulse repetition rate. Of course, when the desired pulse repetition rate is input, the possible pulse width of the setting unit 12 can be displayed for selection.

Claims (12)

A laser producing pulsed laser radiation (2),
A resonator (3);
A laser active medium (6) disposed in the resonator (3);
A Q switch (8) disposed in the resonator (3) and settable in a first state and a second state to set the quality of the resonator; and the quality of the resonator is second in the first state. Lower than condition,
When the Q switch (8) is in the second state, a detector (10) that measures the intensity of the laser pulse being formed and outputs the measured value as an intensity signal (I);
The Q switch (8) is controlled according to the predetermined pulse period and the supplied intensity signal (I), and the Q switch (8) is changed from the second state to the first state before the pulse formation of the laser pulse is completed. A laser comprising a control unit (11) for switching.   The laser of claim 1, wherein the rising or falling intensity value of the laser pulse is related to a predetermined pulse period.   The laser according to claim 1 or 2, wherein the Q-switch (8) is implemented as an acousto-optic modulator or an electro-optic modulator.   The laser according to any one of claims 1 to 3, wherein the control unit sets the pulse period by switching the Q switch (8) from the second state to the first state by an electronic delay. A setting unit (12) connected to the control unit (11) and capable of inputting a predetermined pulse period and a predetermined pulse repetition rate;
The control unit (11) controls the Q switch (8) so that the pulse (14) of the pulsed laser radiation (2) has a predetermined pulse duration and a predetermined pulse repetition rate. The laser according to one item.   The setting unit (12) displays one or more of the possible pulse repetition rates and possible pulse periods for selection, respectively, upon input of one or more of the predetermined pulse periods and predetermined pulse repetition rates. Item 6. The laser according to Item 5. A resonator, a Q switch disposed in the resonator, and a laser active medium, wherein the Q switch can be set to a first state and a second state in order to set the quality of the resonator; A method for generating pulsed laser radiation in a laser in a first state lower than in a second state, comprising:
When the Q switch is in the second state, the intensity of the laser pulse being formed is measured and output as an intensity signal, and before the pulse formation of the laser pulse is completed, depending on the predetermined pulse period and the predetermined intensity signal The method of switching the Q switch from the second state to the first state.   The method of claim 7, wherein the intensity value of the rising edge of the laser pulse is related to a predetermined pulse period.   9. A method according to claim 7 or 8, wherein the Q switch is implemented as an acousto-optic modulator or an electro-optic modulator.   The method according to claim 7, wherein the pulse period is set by switching the Q switch from the second state to the first state by an electronic delay.   The laser includes a setting unit capable of inputting a predetermined pulse period and a predetermined pulse repetition rate, and the Q switch is controlled so that a pulse of the pulse laser radiation has a predetermined pulse period and a predetermined pulse repetition rate. The method according to any one of 10.   The setting unit displays one or more of a possible pulse repetition rate and a possible pulse period for selection when one or more of a predetermined pulse period and a predetermined pulse repetition rate are input, respectively. The method described.

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